Please Help: Extracting WMA channels

Zooya

Hello!

I have an iRiver E100 that is capable of recording audio from its built-in microphone, external microphone and line-in. Most of the time I make recordings with its built-in one which is mono, though the format it's recording is a Stereo WMA, 192kbps and it's a waste of disk capacity, since both audio tracks contain the same material. There is no option adjusting the channels for recording.

I'm looking for a (command line if there's one) tool that can extract one channel from a WMA file and save to another. For instance my 192kbps WMAs consist two 96kbps WMA audio streams, one for each channel (2). I'd like to extract one of these channels to a new file, that'd be Mono and 96 kbps.

I'm pretty sure that audio channels are stored somehow separately. For example, I have a recording, speech-of-my-friend-in-the-school.wma that is 11 682 672 in bytes and 8:04 long (484 seconds). At 192kbps a 484 seconds long audio clip would be (192000*484)/8 = 11 616 000 bytes which is almost the same as the real size (maybe there are more frames than exactly 484 seconds and the real bitrate doesn't end with 000, there's a header, that's why the real size is bigger), so I don't think it spares disk space by summing/differencing audio tracks, because in this case the size should be around half as big as a conventional 192kbps clip.

I have WinAmp and audio editing softwares, but I would not like to convert my clips. I could downmix them and convert them using ffmpeg/lame/etc. but this will result in the loss of quality. The only option for me is copying one channel and saving it as a mono-channel WMA.

Tried using AsfBin, but couldn't figure out how to separate a stereo audio tracks into two mono channels without re-encoding. Tried: asfbin -i <inputfile> -o <outputfile> -nostream 2 , but it handles the audio part as one stream.

Also tried with ffmpeg -i <inputfile> -ab 96k -ac 1 -acodec copy <outputfile>, no success, it generates an output file arund the same size and bitrate as the input.

Thanks in advance
Zooya

Zooya

Anyone here who could help?

olyteddy

You'll likely meet the same folks here as at the other forum you posted this at. How much quality do you imagine you'd lose resampling a voice recording, anyway?

Zooya

That much I can hear with my ears. I've already tried resampling it to a mono MP3 using lame (with these options: -a -b96 -q0). Also tried using mp3sencoder (by Fraunhofer) with options -q 1 -c 1. Surprisingly, Fraunhofer's stuff produced even worse quality than lame.

AllanDeGroot

The only easy way I can think of would be to convert them to WAV (or play them back as analog audio) then compress them as mp3's.

alternatly you could much more easily remove your root concern
(use of excess storage space) by simply getting a larger HDD.


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Zooya

I have a HDD large enough (1TB), there is 100 GB of these recordings which could be 50GB without any quality loss if I could figure out how to extract one channel from them. I won't buy a new HDD, because I don't agree with wasting resources and disk space just because Microsoft wants me to.

Ibex

You could give dBpowerAMP a try. There is a Channel Split utility codec, but the audio is probably re-encoded in the process.

Zooya

Thanks, dBpowerAMP looks like a great app. Although it can't channel split without re-encoding, I was able to convert a bunch of my recordings to mono-equivalent bitrate 96kbps MP3 in batch mode. Unfortunately the result is as bad as I had used lame or mp3sencoder (fraunhofer) from command line.

Ibex

Ah... (If my memory is correct) WMA always uses joint stereo for multi-channel audio files, so lossless splitting of the audio channels is impossible.

I have experienced sound quality problems before when transcoding audio from another lossy codec to MP3. For example, after converting radio comedy programmes from 44Kbit Real Audio 8 to MP3 whenever there was laughter the sound would break up badly and there would be metallic artifacts, even when encoded at a very high MP3 bitrate. Converting to WMA instead solved the problem. Keeping the destination bitrate slightly higher than the source bitrate also helps to maintain sound quality and avoid artifacts.

But, as I am sure you have already discovered, WMA only allows certain combinations of bitrate, sample frequency & channels. For mono at 44KHz the maximum bitrate is only 48Kbit.

You can try converting to AAC or Ogg Vorbis. Both are very good lossy compression codecs and of a similar sound quality to WMA.